40 INCISION OF LEAF [CH. 



putting out its tertiary ribs and veins of various orders as 

 it does so. 



In the other type, the lobes diverge in a more or less 

 radiating manner from the point in the base of the leaf 

 where the petiole joins the lamina, and, as before, each 

 similarly radiating principal rib passes up into a lobe. 

 We thus" get two types of lobing; palmately lobed and 

 pinnately lobed leaves. 



The next point for consideration is the relative sizes 

 of the lobes themselves, or, as it is generally expressed 

 but erroneously the relative depth of the incisions 

 between the lobes into the lamina. If such incision only 

 reaches about half-way from the general contour of the 

 leaf towards the midrib, in pinnately lobed leaves, or 

 towards the base, in palmately lobed leaves, the lamina is 

 described as pinnatifid or palmatifid respectively ; if the 

 incision goes deeper the lamina is pinnatisect or palmatisect, 

 or partite respectively, it being understood that in no case 

 hitherto considered does the incision reach the midrib, or 

 base, and completely cut off the lobe from other lobes. 

 In other words, the green softer tissues of all the lobes 

 are in continuity one with another by however narrow 

 an isthmus of tissue at the bases of the incisions. 



A step further, and the lobing or branching of the leaf 

 is so complete that each segment i.e. branch of the 

 leaf becomes independent of its neighbour, and stands 

 off from the principal midrib of the leaf, or from the 

 point of junction with the petiole at its base, as a separate 

 leaflet, and the whole leaf is now said to be compound, 

 pinnate (Fig. 12), or palmate (Fig. 13), as the case 

 may be. 



In such compound leaves the common or principal 

 midrib, continuous with the petiole, is termed the rachis, 

 and when, as often happens, each leaflet has its own little 



